Hydrocracking technology as one of the primary means for cracking heavy oil has the advantages such as a strong adaptability to raw materials, flexible product schemes, high target product selectivity, excellent product quality, and high added-value, and can satisfy the requirements on clean fuel in the market and has become the main secondary refining technology in the twenty-first century.
Single-stage hydrocracking technology has the advantages of simple process, easy operation, low investment, stable product selectivity and property. In the single-stage hydrocracking technology, since the raw material is in direct contact with the single-stage hydrocracking catalyst without any pre-refining treatment or with a simple pre-refining treatment, the single-stage hydrocracking catalyst is required to have a stronger hydrogenating performance and a stronger resistance to impurities. Meanwhile, the crude oil quality becomes worse year by year, and the refinery begins to apply the crude oil vacuum deep distillation technology in order to increase the economic benefits, so that the end boiling point of the vacuum distillate is increased from 520° C. to about 600° C. Due to the increasing density, increasingly high distillation range, increasing molecular weight of the hydrocarbon molecules contained therein, increasingly complex structure, and increasing amounts of impurities such as sulfur and nitrogen, the difficulties of hydrocracking treatment are greatly increased, which presents the increasingly higher requirements on hydrocracking technology and hydrocracking catalysts, in particular higher requirements on the single-stage hydrocracking catalyst.
Without protection by hydrogenation pre-refining catalyst, the single-stage hydrocracking catalyst is in direct contact with a plurality of organosulfides and organonitrides. Thus the catalyst is required to necessarily have a very high hydrodenitrogenation activity, a very high hydrodesulfurization activity and a hydrosaturation performance, so as to maintain the sufficient exertion of the catalyst performance. The hydrogenation performance of the hydrocracking catalyst having a conventional metal amount (the total amount of the hydrogenation metal is generally lower than 30% calculated by the oxides) cannot satisfy the actual use requirements on the single-stage hydrocracking catalyst.
Hydrocracking catalysts are generally prepared by the impregnation method, the co-precipitation method and the comulling method. As stated in CN01123767.8, U.S. Pat. No. 6,527,945, CN00110016.5, CN00109747.4 and U.S. Pat. No. 5,565,088, when the impregnation method is used to load active components, the specific surface area and pore volume of the catalyst support are obviously influenced. Thus the amount of the active components is limited, and generally no more than 30 wt. %; otherwise, the specific surface area and pore volume will not satisfy the requirements on the single-stage hydrocracking catalyst. Hydrocracking catalysts having a very high active metal amount can be obtained by the co-precipitation method. As stated in U.S. Pat. No. 5,086,032, U.S. Pat. No. 4,820,677 and CN200410050730.9, the metal amount may be as high as 50%-95%. The catalyst prepared by the co-precipitation method has a smaller pore volume and specific surface area, and can only be used for treating distillates lighter than diesel oil. Moreover, since the catalyst prepared by the co-precipitation method has a low metal utilization, a bad metal dispersion capability, a complex preparation process, and a worse product stability, the catalyst has a low cost performance. The comulling method can be used for preparing the catalyst having various active metal amounts. However, the catalyst prepared by the kneading method has a relatively worse performance, a low specific surface area and a low active metal utilization, so that it has been less used.
The single-stage hydrocracking catalyst is generally required to have a higher active metal amount, and to have a higher specific surface area and a pore volume at the same time. However, the aforesaid current methods cannot simultaneously satisfy these two requirements. That is to say, the hydrocracking catalyst having a high hydrogenation active metal amount, a high pore volume and a specific surface area at the same time cannot be obtained according to the prior art.